The present inventive concept relates to a semiconductor device and a fabricating method thereof.
As the size of metal oxide semiconductor (MOS) transistors are decreased, the length of a gate and the length of a channel formed below the gate are also reduced. Accordingly, various efforts have been made to increase the capacitance between the gate and the channel to improve the operating characteristics of the MOS transistor.
A silicon oxide film that is typically used as a gate insulating film has physical limitations in the electrical properties as the thickness is reduced. Accordingly, the use of high dielectric constant (high-k) films that have a high dielectric constant have been investigated as a replacement for silicon oxide gate insulating films in MOS transistors. When such high-k films are used, it is possible to reduce leakage current between a gate electrode and a channel region while using a thin equivalent oxide film.
Further, polysilicon which is typically used as a gate material, has a resistance that is larger than the resistance of most metals. Thus, the polysilicon gate electrode is being replaced by a metal gate electrode in many MOS transistors.